How do I fix (idle) that shows up in the Chrome JavaScript Profiler?

I have a JavaScript script in an Angular page that executes a promise chain as follows:

foo().then(() => {
    console.profile("foo1");
    ...
    return foo1();
}).then(() => {
    console.profileEnd("foo1");
    console.profile("foo2");
    ...
    return foo2();
}).then(() => {
    console.profileEnd("foo2");
    console.profile("foo3");
    ...
    return foo3();
})
...

I use console.profile to find out which part of the promise chain takes so much time to execute. What I noticed is that one of the profilers (in my case foo6) has a 350ms idle time. What is a good approach to find out why it is not executing anything although the promise chain has still not finished?

from How do I fix (idle) that shows up in the Chrome JavaScript Profiler?